The present invention relates to the use of solenopsin A and its analogs as angiogenesis inhibitors.
Angiogenesis may be defined as the development of a blood supply to a given area of tissue. The development of a blood supply may be part of normal embryonic development, represent the revascularization of a wound bed, or involve the stimulation of vessel growth by inflammatory or malignant cells. Sometimes angiogenesis is defined as the process through which tumors or inflammatory conditions derive or create a blood supply through the generation of microvessels. Although it may seem unremarkable that new growth of soft tissue requires new vascularization, the concept of angiogenesis as a key component of tissue growth and in particular, a key point of intervention in pathological tissue growth, had initially met with skepticism. By now the idea is well accepted.
Tumors need to induce formation of blood vessels to grow beyond a small size. A small tumor can use diffusion from nearby capillaries as its source of oxygenation, nutrition, and waste removal. However, once a tumor exceeds a critical mass, the center of the tumor becomes necrotic, because these crucial functions are no longer available. When a tumor gains the ability to generate new blood vessels, perfusion of a larger tumor mass is possible. The ability of malignant cells to form a large tumor and to metastasize is accompanied by decreased cellular differentiation and increased ability to produce angiogenic factors, which results in greater vascularization. There is therefore a strong interest in compounds that block angiogenesis and interrupt the growth process of malignant tumors, inflammatory lesions and benign neoplasms, as well as in compounds which stimulate cellular differentiation, and impede metastasis.
A tumor's ability to become neovascularized permits rapid tumor growth and increases the likelihood of metastases; the transition from a quiescent tumor to an invasive tumor is accompanied by the crucial acquisition of angiogenic properties. The critical point may be characterized as the activation of a specific angiogenic switch. The phenotypic change from quiescence to virulence likely requires a change in the balance of angiogenic simulators and angiogenic inhibitors. The nature of the angiogenic switch is not known, however, growth factors and signal transduction are expected to be key components in the investigation of angiogenic regulatory mechanisms.
Historically, the first angiogenesis factor isolated was basic fibroblast growth factor (bFGF). Others include vascular endothelial growth factor (VEGF), interleukin-8, hepatocyte growth factor, platelet derived endothelial growth factor (PD-ECGF), and corticotropin-releasing hormone (CRH). The discovery of endogenous angiogenesis simulators naturally led researchers to ask whether there existed endogenous angiogenesis inhibitors. Interferon-alpha, which inhibits the replication of primary endothelial cells, was the first endogenous angiogenesis inhibitor discovered. Other naturally occurring small molecules which have been discovered to have anti-angiogenic activity include the retinoids and curcumin, a small molecular weight compound which is isolated from the commonly used spice turmeric. Recently, a number of chalcone analogs have been synthesized and have been shown to exhibit activity as anti-angiogenic agents.
Among the angiogenisis inhibitors, retinoids (vitamin A and its derivatives) play an important role in the development and differentiation of epidermal cells, as well as in reversing precancerous lesions. A number of references disclose retinoids being used in cancer prophylaxis and as inducers of cell differentiation. Kizaki et al., Seminars in Oncology 19(1):95-105 (1992), for example, report that retinoids are potential anti-carcinogenic agents in many experimental models and that they inhibit growth and induce differentiation in transformed neoplastic cells.
The solenopsins are piperidine alkaloids which are derived from the venom of the red fire ant Solenopsis invicta. The venom of this insect consists of 95% alkaloids and the remainder contains solubilized proteins, amino acids and enzymes including hyaluronidase and phospholipase. Among the piperidine alkaloids, the two major components are Solenopsin A, a trans-2-methyl 6-n-undecylpiperidine and Solenopsin B, a 2,6-trans-dialkyl-piperidine.
Recently, a number of novel solenopsin analogs have been synthesized and presented as inhibitors and/or suppressants of fire ants and other insects. Another use of the solenopsins is for the elimination of ticks, fleas or other parasitic infections in dogs and cats as disclosed by Rehmert, et al. in U.S. Pat. Nos. 4,910,209, 5,075,320, and 5,098,914. In this approach, the solenopsins are administered as the whole body extract of the insect or from an oral dosage form containing more highly purified material. The administration of these drugs over a period of one to eleven days with regular booster dosages disseminates the alkaloid composition through the blood and tissue fluids of the treated animals and eliminates fluid-feeding parasites.
In the whole body version, the insects are ground to a fine texture, inserted into soluble capsules as whole body extract along with an edible carrier material such as fish oil, and are kept frozen until administration. The venom is kept refrigerated in order to maintain its effectiveness. Additionally, each insect is considered to contain approximately one venom unit or 40 nanoliters of the solenopsins, Solenopsin A and Solenopsin B.
Typically, 100-400 units of such extracts are given consecutively to dogs weighing four to 120 pounds over 11 days. However, day two is skipped to allow the animal to react to the dosage. Complete elimination of tick and flea infestation was achieved. Similarly, 100-200 units were administered in cats as well and resulted in same results. Booster doses are also given monthly in order to prevent re-infestation of such parasites.
Synthetically produced Solenopsin A is effective as well and results in complete elimination of blood and tissue- and fluid-feeding parasites. Unlike the whole body extract, it does not require refrigeration. However, higher number of units of the synthetic version are required for effective treatment. For example, 1500 units of synthetically produced Solenopsin A are equivalent to 250 units of the whole body extracts. As much as 6000 units of Solenopsin A has been used over a shorter time period and did not cause any ill effects.
Oral dosage capsules in the range of 1500 units are typically prepared by mixing 50-60 microliters of Solenopsin A with 0.1 ml of isopropylalcohol, 20 mg of fumed silica and 150 mg of microcrystalline cellulose as a carrier material. They are then packaged into soluble capsules.
The solenopsins have demonstrated low toxicity and also have shown to be more effective than the organophosphates whose efficacy has decreased due to the development of resistance in parasites. Furthermore, they are also excellent alternatives to the organophosphates which are toxic to cats.